Handheld power tool

ABSTRACT

The invention is based on a handheld power tool having a motor ( 10 ), a planetary gear ( 12 ) and a tool receptacle ( 4 ).  
     It is proposed that the handheld power tool includes an air-moving means ( 46, 78 ), located upstream the motor ( 10 ), out of sight of the tool receptacle (4), for generating a cooling air stream that cools the planetary gear ( 12 ).

PRIOR ART

The invention is based on a handheld power tool as generically definedby the preamble to claim 1.

Cordless drills or cordless screwdrivers are as a rule very compact inconstruction, and for stepping down the speed they have a single—ormulti-stage planetary gear. Factors that argue for a planetary gear areits compact construction that can readily be integrated ergonomicallyinto the handheld power tool, as well as its capability of transmittinghigh outputs with great sturdiness and running smoothness. One suchcordless screwdriver is known from German Patent Disclosure DE 197 37234 A1, for instance.

ADVANTAGES OF THE INVENTION

The invention is based on a handheld power tool having a motor, aplanetary gear and a tool receptacle.

It is proposed that the handheld power tool has an air-moving means,located upstream of the motor, out of sight of the tool receptacle, forgenerating a cooling air stream that cools the planetary gear. As aresult, while maintaining the structural design with a planetary gear, agear with very high output and at the same time a long service life canbe attained. By locating the air-moving means upstream of the motor,that is, in particular in the immediate vicinity of the planetary gear,effective cooling of the planetary gear can be achieved. The motor ofthe handheld power tool can additionally be cooled with a furtherair-moving means out of sight of the tool receptacle, downstream of themotor. In such a construction, by the provision of two air-moving means,air-carrying conduits around the motor can be dispensed with, and thering gear can be made especially compact. The air-moving means forcooling the planetary gear can serve solely to cool the planetary gear,or it may for instance be provided for additional cooling of the motor.The air-moving means is expediently a rotating air-moving means. Becauseof the compact design, the invention is especially well suited to acordless handheld power tool, in particular a cordless screwdriver,cordless drill/screwdriver, or cordless impact drill/screwdriver.

If an autolock device is used that very quickly stops the engine fromrunning on after the power supply has been interrupted by a user, thenbecause of the sudden braking, very high forces may engage thehigh-speed air-moving means. An especially sturdy construction can beachieved by the designing the air-moving means as a fan wheel. Blades ofthe fan wheel can be joined together by a wheel —expediently solely ontheir radially outer end—thus lending the fan wheel high rigidity.

In an advantageous feature of the invention, the air-moving means isintegrated with the planetary gear. As a result, the gear can beinstalled together with the air-moving means as a structural unit in thehandheld power tool, thus lessening the effort and expense of assembly.Moreover, with this kind of disposition, the location where heat isproduced, namely where the planet wheels are, is cooled especiallyeffectively.

Expediently, the air-moving means is located between the motor and agear stage of the planetary gear. As a result, it can be driven before aspeed reduction and can thus be driven at high rotary speed.

An especially simple rotational slaving of the air-moving means can beattained if it is connected to a motor pinion in form-locking fashion. Aform-locking geometry of the motor shaft for driving the air-movingmeans can be dispensed with, and in this way the motor shaft can bedesigned economically. The form lock can be produced especially simplyif the teeth of the motor pinion mesh with a corresponding counterpartshape of the air-moving means.

Stable concentricity of the air-moving means can be attained if theair-moving means is braced on the motor shaft. The rotational slaving isadvantageously achieved here via the form lock with the motor pinion andthe stability of concentricity is achieved by the direct bracing on themotor shaft. Thus in a simple way, simple assembly, with structuralunits of the handheld power tool that are economical to produce, andwith an air-moving means that runs in a stable way, can all be attained.

In a further feature of the invention, it is proposed that theair-moving means is intended for generating a cooling air stream throughthe planetary gear. As a result, heat produced in the planetary gear canbe especially effectively dissipated from the planetary gear. Theplanetary gear expediently includes a housing, which has at least oneopening upstream and one opening downstream of the inner planetary gearcomponents. The directions “upstream” and “downstream” refer to a viewlooking in the direction away from the tool receptacle.

It is furthermore proposed that the handheld power tool has a housing,with at least one first and second ventilation opening, and aventilation conduit which extends continuously from the firstventilation opening through the planetary gear to the second ventilationopening. The housing is advantageously an outer housing, so that airfrom outside the handheld power tool can flow through the planetarygear. The ventilation conduit expediently experiences a flow through itin one direction during operation of the handheld power tool. Especiallygood heat dissipation from the planetary gear can be achieved if thefirst and second ventilation openings are located upstream anddownstream, respectively, of at least one element of the planetary gear.

Good cooling of the planet wheels can be attained if the planet wheelsare supported on a retaining means which has openings, extending in theaxial direction, in a radial region of the planet wheels. These openingsare for instance next to the planet wheels in the circumferentialdirection.

By means of a ventilation conduit that extends continuously from acoupling region of the handheld power tool to the motor, the planetarygear can experience an especially complete flow through it, and heat canbe especially well dissipated.

A high cooling output of a gear wheel of the planetary gear can beachieved if the air-moving means is located in the immediate vicinity ofthe gear wheel. The gear wheel is for instance a planet wheel. Theimmediacy is preserved if a narrow air gap, for assuring a difference inmotion, remains between the gear wheel and the air-moving means.However, this air gap is free of components.

A cordless screwdriver is typically used in both directions of rotation.Cooling of the planetary gear is therefore especially effective if theair-moving means is rotatable in two directions of rotation andgenerates an air stream in the same direction in both directions ofrotation. The air flow direction is thus independent of the direction ofrotation of the handheld power tool or of the air-moving means. Theair-moving means may have blades for this purpose, whose blade faces areoriented perpendicular to the directions of rotation. It is especiallyadvantageous for the blades to be embodied with at least two bladefaces; one blade face, in a first direction of rotation, directs the airat least partly in an axial direction, and the other blade face, in asecond direction of rotation opposite the first direction of rotation,directs the air at least partly in the same axial direction.

Good ventilation geometry together with high strength of the air-movingmeans can be attained if the air-moving means includes blades whoselength in one direction of rotation is greater than their length in theaxial direction.

In an advantageous refinement of the invention, the air-moving meansgenerates an air stream directed in the radial direction and includes adeflection means for deflecting the air stream in the axial direction.It suffices here if the air stream is initially directed only at leastpartly in the radial direction. The deflection means is advantageouslypart of the air-moving means and is rotatable with it and can be formedas a chamfer on a wheel that holds the blades of the air-moving meanstogether on their radially outer end.

DRAWINGS

Further advantages will become apparent from the ensuing description ofthe drawings. In the drawings, exemplary embodiments of the inventionare shown. The drawings, description and claims include numerouscharacteristics in combination. One skilled in the art will expedientlyconsider the characteristics individually as well and put them togetherto make useful further combinations.

Shown are:

FIG. 1, a fragmentary view of a cordless screwdriver with a housingshell removed;

FIG. 2, the removed housing shell of the cordless screwdriver from FIG.1;

FIG. 3, an exploded view of a motor, a gear cover disk, an air-movingmeans, and a motor pinion;

FIG. 4, a sectional view through part of the cordless screwdriver ofFIG. 1 and the elements of FIG. 3;

FIG. 5, a further air-moving means in the form of a fan wheel; and

FIG. 6, the fan wheel of FIG. 5 seen from the front.

FIG. 1 shows a handheld power tool in the form of a cordless screwdriver2, with a tool receptacle 4 shown in suggested form, and with a housingthat includes two housing shells 6 and one front housing element 8. Oneof the housing shells 6 is shown by itself in FIG. 2. Located inside thehousing shells 6 is a motor 10, which is connected to a rear air-movingmeans, in the form of a fan wheel, that is not shown in the drawings.Upstream of the motor 10, looking from the tool receptacle 4, there is aplanetary gear 12, which is shown in section in FIG. 4. In FIG. 1, whatcan be seen of the planetary gear 12 is a gear shifter 18, with anopening 16 serving as an air conduit.

The motor 10 includes a motor shaft 20 (FIGS. 3 and 4), onto which agear wheel in the from of a motor pinion 22 is thrust. The motor pinion22 forms part of the planetary gear 12 and drives planet wheels 24,which roll along the inside of a ring gear 26. As a result, a sun wheel28 is rotated, which in turn, via toothing 30, drives further planetwheels 32, which roll in a second ring gear 34. The planet wheels 32 ofthe second gear stage drive a further sun wheel 36.

The planetary gear 12 is essentially closed off from the outside by agear plate 39 in conjunction with the sun wheel 36, the gear sleeve 14,and a retaining disk 40. The retaining disk 40 is connected to the gearsleeve 14 via a form lock and brings about the rotational locking of themotor 10 in the gear sleeve 14 as well as axial spacing, by means ofspacers 41, of the ring gear 26 of the first planetary gear stage.

Both between the sun wheel 36 and the gear plate 39 and in the retainingdisk 40, openings 42, 44 are made for enabling an air stream through theplanetary gear 12. This air stream is driven an air-moving means 46,which is designed as a fan wheel. The fan wheel is located predominantlyinside the planetary gear 12 and is driven to rotate by the motor pinion22 by means of a form lock with a neck 48 of the motor pinion 22. Thefan wheel is located on the neck 48 by means of a clearance fit, inorder to permit certain tolerances. In order to avoid an imbalance ofthe fan wheel despite these tolerances and even if there is a slightdeviation from this clearance fit upon major acceleration of theair-moving means 46, the fan wheel is supported primarily directly onthe motor shaft 20 in a concentric bearing seat 50 and is kept centeredby the motor shaft 20. In the region of this bearing seat 50, theair-moving means 46 is located between the planetary gear 12 and abearing 52 of the motor shaft 20. Outside this bearing seat 50, the fanwheel is located between the retaining disk 40 and the planet wheels 24,or in other words inside the planetary gear 12.

To maintain a spacing between the fan wheel and the planet wheels 24 andbetween the fan wheel and the ring gear 26, a runup disk 53 is locatedbetween the fan wheel and the planet wheels 24. Upon a rotation of thefan wheel, an air stream primarily in the radial direction 58 isgenerated by twelve blades 56 of the fan wheel that are oriented in theaxial direction 54; this air stream is deflected at least partly in theaxial direction 54, specifically in the direction toward the motor 10,by oblique faces 60, which are integrally formed onto a wheel 62 thatholds the blades 56 together on the radially outer end of each of theblades. An air stream moved in this way is forced through the openings44 in the retaining disk 40 in the direction of the arrow 64 toward themotor 10 and along this motor. In its further course, this air stream isdeflected out of ventilation openings 66 in the housing shells 6 and outof the handheld power tool.

Because of this air stream, an underpressure is generated inside theplanetary gear 12, and by means of it air is aspirated throughventilation openings 68 in the housing shells 6. This air stream,through the openings 16 in the gear shifter 18, flows under the gearshifter 18 and through switching spring openings 70 in the gear sleeve14, through the gear sleeve 14, into the interior of the planetary gear12, as indicated by an arrow 72. This air stream can flow over the ringgears 26, 34 from outside and in this way cools the planetary gear 12.The handheld power tool 26 is supported inside the gear sleeve 14 byfour supporting arms, which are not visible in the sectional view shownin FIG. 4. Instead, hollow chambers 74 between the supporting arms canbe seen, through which the air stream can flow.

Because of the underpressure generated in the planetary gear 12 by theair-moving means 46, a further air stream, represented by an arrow 76,is steered out of the coupling region 38 through the openings 42 intothe interior of the planetary gear 12. This air stream can flow directlyaround the planet wheels 24, 32 of both gear stages of the planetarygear 12 and thus effectively cool them.

FIGS. 5 and 6, in a view from the back and the front, respectively, showa further air-moving means 78. This air-moving means 78, again designedas a fan wheel, can be connected in form-locking fashion to the motorpinion 22 by means of a clearance fit 80 shaped as a negative of thetooth form to fit the toothing of the motor pinion 22 and is carriedalong by the motor pinion in the tangential direction 82. In the rearand radially inner region, the air-moving means 78 includes a furtherfit 84 for being supported directly on the motor shaft 20. Theair-moving means 78 includes eight blades 86, which each have one firstand one second oblique, concave blade face 88, 90. In clockwiseoperation of the handheld power tool, the air stream is forced radiallyoutward and axially rearward by the first blade face 88. The portion ofthe air stream forced radially outward is also forced to the rear in theaxial direction 54 by a concave oblique face 92 of a wheel 94 thatconnects the radially outer ends of the blades 86. In this way, inclockwise operation, an air flow directed inward is produced, whichcools the planetary gear 12 as described above. In counterclockwiseoperation, the second blade face 90 forces the air stream radiallyoutward and axially rearward, so that in an analogous way, an air streamto the rear—and thus because of the draft, an air stream through theplanetary gear 12—is generated.

List of Reference Numerals

-   2 Cordless screwdriver-   4 Tool receptacle-   6 Housing shell-   8 Housing element-   10 Motor-   12 Planetary gear-   14 Gear sleeve-   16 Opening-   18 Gear shifter-   20 Motor shaft-   22 Motor pinion-   24 Planet wheel-   26 Ring gear-   28 Sun wheel-   30 Toothing-   32 Planet wheel-   34 Ring gear-   36 Sun wheel-   38 Coupling region-   39 Gear plate-   40 Retaining disk-   41 Spacer-   42 Opening-   44 Opening-   46 Air-moving means-   48 Neck-   50 Bearing seat-   52 Bearing-   53 Runup disk-   54 Axial direction-   56 Blade-   58 Radial direction-   60 Oblique face-   62 Wheel-   64 Arrow-   66 Ventilation opening-   68 Ventilation opening-   70 Switching spring opening-   72 Arrow-   74 Hollow chamber-   76 Arrow-   78 Air-moving means-   80 Clearance fit-   82 Tangential direction-   84 Fit-   86 Blade-   88 Blade face-   90 Blade face-   92 Oblique face-   94 Wheel

1. A handheld power tool having a motor (10), a planetary gear (12) anda tool receptacle (4), characterized by an air-moving means (46, 78),located upstream the motor (10), out of sight of the tool receptacle(4), for generating a cooling air stream that cools the planetary gear(12).
 2. The handheld power tool as defined by claim 1, characterized inthat the air-moving means (46, 78) is integrated with the planetary gear(12).
 3. The handheld power tool as defined by claim 1, characterized inthat the air-moving means (46, 78) is located between the motor (10) anda gear stage of the planetary gear (12).
 4. The handheld power tool asdefined by claim 1, characterized in that the air-moving means (46, 78)is provided for generating a cooling air stream flowing through theplanetary gear (12).
 5. The handheld power tool as defined by claim 1,characterized by a housing having at least one first and one secondventilation opening (66, 68) and at least one ventilation conduit, whichextends continuously from the first ventilation opening (68) through theplanetary gear (12) to the second ventilation opening (66).
 6. Thehandheld power tool as defined by claim 1, characterized by a couplingregion (38) and at least one ventilation conduit that extendscontinuously from the coupling region (38) to the motor (10).
 7. Thehandheld power tool as defined by claim 1, characterized in that theair-moving means (46, 78) is located in the immediate vicinity of a gearwheel of the planetary gear (12).
 8. The handheld power tool as definedby claim 1, characterized in that the air-moving means (46, 78) isrotatable in two directions of rotation and in both directions ofrotation generates an air stream in the same direction.
 9. The handheldpower tool as defined by claim 1, characterized in that the air-movingmeans (78) has blades (86) with at least two blade faces (88, 90), andone blade face (88), in a first direction of rotation, directs the airat least partly in an axial direction (54), and the other blade face(90), in a second direction of rotation opposite the first direction ofrotation, directs the air at least partly in the same axial direction(54).
 10. The handheld power tool as defined by claim 1, characterizedin that the air-moving means (46, 78) generates an air stream directedin the radial direction (58) and includes a deflection means fordeflecting the air stream in the axial direction (54).